The present invention relates to a catalytic process for the production of high-octane gasoline from a hydrocarbon feed stream comprising C4+ hydrocarbon cuts in presence of a catalyst composition comprising mixed aluminium and zirconium oxides modified with tungsten oxyanion and hydrogenation/dehydrogenation component of a Group VIII metal.
Multi-branched paraffins are ideal gasoline-blending components possessing high octane numbers. For environmental reasons, there is also a need to find substitutes for aromatic components in gasoline. Therefore, there is an incentive to develop a process for increasing the octane number of the C4-C12 cuts. While C5/C6 paraffin isomerisation is a common refinery process, commercialisation of processes including higher fractions (C7+ hydrocarbons) meets significant difficulties given by the usually high degree of cracking to gas.
An article by K. Arata and M. Hino in Proceedings 9th International Congress on Catalysis (1988) describes a catalyst based on a Group IVB metal oxide such as zirconia in particular, modified by the oxyanion of the Group VIB, particularly tungstate and its use in paraffin isomerisation.
U.S. Pat. No. 5,510,309 provided a method for preparing an acidic solid comprising a Group IVB metal oxide modified with an oxyanion of a Group VIB metal. An example of this acidic solid is zirconia modified with tungstate. This modified solid oxide may be used as a catalyst for example to isomerise C4 to C8 paraffins. The modified solid oxide is prepared by co-precipitating the Group IVB metal oxide along with the oxyanion of the Group VIB metal. Aluminium is mentioned merely as a conventional matrix material such as alumina, silica-alumina and silica with preference given to silica.
Use of tungstated zirconia promoted with noble metal in paraffin isomerisation was described in open literature—S. L. Soled, S. Miseo, J. E. Baumgartner, W. E. Gates, D. G. Barton and E. Iglesia, in: Proc. 13th Int. Conf. Catal. (The Taniguchi Foundation, Kobe, Japan, 1994) page 17; E. Iglesia, D. G. Barton, S. L. Soled, S. Miseo, J. E. Baumgartner, W. E. Gates, G. A. Fuentes and G. D. Meitzner, Stud. Surf. Sci. Catal. 101 (1996) 533; G. Larsen, E. Lotero, S. Raghavan, R. D. Parra and C. A. Querini, Appl. Catal. A 139 (1996) 201.
The tungstated zirconia system was frequently described as catalyst for C5+ isomerisation. The following patents are variations of the above-mentioned prior art. The catalyst typically contained tungsten oxide in a concentration below 20 wt % and hydrogenation component is platinum. Selectivity of these materials is not sufficient to reach liquid yields above 90% for C7+ isomerisation when approaching composition given by thermodynamics. U.S. Pat. No. 5,422,327 describes a catalyst composition of a Group VIII metal incorporated into a support consisting of zirconia, said support being further impregnated with a mixture of silica and tungsten oxide and its use in paraffin isomerisation. U.S. Pat. No. 5,648,589 claims a catalytic isomerisation process comprising contacting a C5+ feed under isomerisation conditions with a catalyst composition consisting of a Group VIII metal and a zirconia support impregnated with tungsten oxide and silica. U.S. Pat. No. 5,780,382 provides a method for preparing an acidic solid comprising a Group IVB metal oxide modified with an oxyanion of a Group VIB metal. U.S. Pat. No. 5,837,641 describes an isomerisation reaction over tungstated zirconia and the promotional effect of water on this catalyst. U.S. Pat. No. 6,080,904 describes a C4-C8 isomerisation process utilising an isomerisation catalyst with a hydrogenation/dehydrogenation component (preferentially Pt) and with solid acid component comprising a Group IVB metal oxide modified with an oxyanion of a Group VIB metal.